This invention relates generally to the formation of filament products and more particularly a method and apparatus for making filaments and fibrous products therefrom.
It has already been proposed - particularly in French Pat. No. 707 191, U.S. Pat. No. 1 975 504, and Swiss Pat. No. 537 205 to produce relatively short fibers by means of approximately 10% dielectric solutions, very small quantities of which are removed by means of a moving unit which extends partially into a stock of solution in order to wet its surface with the solution. This movable unit constitutes an electrode opposite which at least one counter electrode is arranged. By applying a difference in potential between the electrode and the counter electrode, the electric field developed produces, at the dielectric solution wetting the surface of the electrode, electrostatic forces which propel the liquid entrained out of the stock of solution by the emerging portion of the movable unit towards the counter electrode, forming small fibers. The action of the electrostatic field on the liquid causes a sort of atomization of the liquid.
It is furthermore known that in the case of French Pat. No. 707 191 and U.S. Pat. No. 1 975 504 the movable unit is formed of a toothed wheel, the fibers being started at the ends of the tips of the teeth due to the concentrations of the electrostatic field on these tips.
In Swiss Pat. No. 537 205, the movable unit consists of a ring of a diameter of 1 meter driven at a speed of rotation of 30 rpm corresponding to a speed of about 1.5 meters/second. Taking into account the fluidity of the solutions used, it can be thought that the centrifugal force contributes to the spraying of the liquid into the electric field created between the electrodes.
Moreover, the applications of these processes are very limited and raise numerous practical problems. These limits result from various factors. First of all, the material which can be used must be capable of being transformed into a solution.
The fact that a solution is used raises two contradictory problems. The solution must be sufficiently fluid in order that upon its transportation by the movable unit the solvent does not evaporate before the solution is brought into the electrical field. From the moment that the fiber detaches itself from the movable unit it is projected towards the counter electrode so that the distance between the electrodes must be sufficient to permit the solvent to evaporate in the space between the electrodes, as otherwise the fiber would again form a droplet upon contacting the counter electrode, which would be equivalent to a transportation of liquid from one electrode to the other. The large distance which must separate the electrodes results in the use of voltages of between 50 and 200 KV. These limits of the process extend also to the product obtained, which can be formed only of relatively short fibers.
It has already been proposed to produce by this method products having the appearance of a fabric as well as filters. However, in view of the length of the fibers and the fact that these fibers must be dried before coming into contact with each other, the coherence of the product is insufficient for the formation of a non-woven fabric.